Tweedledum and Tweedledee
Agreed to have a battle;
For Tweedledum said Tweedledee
Had spoiled his nice new rattle.
Just then flew down a monstrous crow,
As black as a tar-barrel;
Which frightened both the heroes so,
They quite forgot their quarrel.
The words Tweedle-dum and Tweedle-dee make their first appearance in print in an epigram by John Byrom (1692–1763) where they seem to be onomatopoeic representations of similar musical phrases:
Some say, compar’d to Bononcini
That Mynheer Handel’s but a Ninny
Others aver, that he to Handel
Is scarcely fit to hold a Candle
Strange all this Difference should be
‘Twixt Tweedle-dum and Tweedle-dee!
(from Wikipedia)